Twin spacecraft are poised Monday to hit a mountain near the moon's north pole after nearly a year in orbit. NASA planned this crash to avoid striking the Apollo landing sites or any other place on the moon with special importance.

The spacecraft known as Ebb and Flow have been measuring the moon's gravity to better understand its interior and early history. To collect data, they've had to circle low above the lunar surface. They're running out of fuel so NASA will command them to hit the surface.

Since this will occur on the dark side of the moon, the space agency says skygazers on Earth won't be able to see it.